1. Field of the Invention
The present invention relates to a lithotrity apparatus utilizing an electromagnetic induction type shock-wave source, and a lithotrity apparatus utilizing an underwater discharge type shock-wave source, both of which pulverize a stone in a patient's body by irradiating the stone with a shock-wave.
2. Description of the Related Art
In a recent treatment of a stone mainly in a kidney or a gall bladder, a method of pulverizing the stone without operation for a patient's body by using a shock-wave has been widely used. As a shock-wave source an underwater discharge type, electromagnetic induction, micro explosion type, and piezoelectric type are proposed. Among them, lithotrity apparatuses of underwater type and micro explosion type have the following arrangement. A shock-wave is generated by a shock-wave source arranged at the first focal point on an ellipsoidal reflecter and is focused on the second focal point. The shock-wave irradiates a stone positioned at the second focal point.
FIG. 6 shows an applicator of a lithotrity apparatus using an electromagnetic induction type shock-wave source, which is a typical example of an electromagnetic induction type lithotrity apparatus. In an electromagnetic induction type shock-wave source 60, a flatly wound coil 61, an insulating sheet 62, and a conductive plate 63 are arranged in parallel to each other and to be extremely close to each other. The coil 61 is connected to a drive circuit (not shown). When a steep high-voltage pulse is momentarily applied to the coil 61, the coil 61 momentarily generates an intense magnetic flux. Since the magnetic flux penetrates the conductive plate 63, an eddy current is generated in the conductive plate 63 in a direction to cancel the magnetic flux. As a result, an intense repulsive force is generated between the coil 61 and the conductive plate 63 to emit an intense plane wave into water 64 contacting the conductive plate 63. The plane wave is focused on a focal point 66 by an acoustic lens 65. At this time, the pressure wave (plane wave) induces water non-linearity as it propagates in the water 64, and is then changed to a shock-wave at the focal point 66. When the position of the focal point 66 coincides with that of a stone, pulverization is performed.
This method is more advantageous than a piezoelectric type method in that a high-power output can be obtained with a comparatively small shock-wave source.
However, in a lithotrity apparatus which uses a piezoelectric as the shock-wave source, echo signals which are reflected by a focal zone can be received and derived as an electrical signal.
Published Unexamined Japanese Patent Application No. 60-191250 and Japanese Patent Application No. 61-149562 propose a lithotrity apparatus having a missed-shot preventive function. According to this apparatus, the feature of a piezoelectric type lithotrity apparatus is utilized. A piezoelectric sends a weak ultrasound immediately before an intense shock-wave is generated. When intense echoes of the ultrasound are received, it is determined that the focal point of the ultrasonic wave coincides with the stone. In this state, a shock-wave for pulverizing the stone is emitted. With this mechanism, a calculus treatment can be performed without erroneously irradiating a normal tissue other than a stone with a shock-wave. As a result, a side effect can be decreased and the pulverizing efficiency can be improved.
In addition to the lithotrity apparatus having the above-mentioned mechanism, in another lithotrity apparatus, an electromagnetic induction type shock-wave source is used, and the shock-wave source uses a rotating elliptic reflecting mirror. In the apparatus having this mechanism, it is checked by using X-rays whether a stone is aligned with the focal point. Then, a shock-wave continuously irradiates the stone while keeping synchronism with an ECG trigger. With this method, however, boresighting cannot catch up with a shift in position of the stone as the is breathing. Therefore, a shock-wave may erroneously irradiate a normal tissue other than the stone, damaging the normal tissue.
In general, an electromagnetic induction type lithotrity apparatus can generate a high-power output with a comparatively smaller shock-wave source than that of a piezoelectric type lithotrity apparatus. It is also easier to control various conditions of the shock-wave than those in an underwater discharge type lithotrity apparatus.
In the electromagnetic induction type lithotrity apparatus using the electromagnetic induction type shock-wave source described above or an underwater discharge type lithotrity apparatus, however, echoes from the inside of the patient's body cannot be received. Therefore, such an apparatus cannot incorporate a missed-shot preventive function based on detection of an echo intensity.